THE LATERAL LINE
The lateral line contains neuromasts: small organs with sensory cells bearing hair-like projections. Water movement bends a jelly-like material covering them, stimulating these cells.
These sensors lie on the skin or in small canals. They detect water moving close to the animal. Fish are not the only animals with this system: some aquatic amphibians have it too.
HOW IT WORKS
A moving animal displaces water and produces disturbances. If these reach the neuromasts, they can inform a fish about nearby movement, even in darkness.
The response depends on the situation. The fish may escape, turn or show no response. The lateral line alone does not identify every predator or provide an infallible alarm: vision and hearing may also contribute.
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